P300
Thread Starter
7th Gear
Joined: Jan 2010
Posts: 7
Likes: 0
P300
I've been reading the posts on this code and it sounds like it could be a few things. Let me start by telling you that I changed the spark plugs and wires and one coil pack for cylinder 5. The orginal code kept coming up p305 which pointed me to this cylinder. Now after the coil pack it's reading p300. I'm baffled by this and would like any help on this topic that anyone would share.
Burning Brakes
Joined: Oct 2008
Posts: 898
Likes: 25
From: Dallas, TX
Hey dj,
Please post up the What your driving, year, Z06 or not, mods etc. Also reset your DIC codes and then drive it and repost all code that come up.
I can tell you that I went down the same road and it ended up being a bad cat on the drivers side. It was covered under the original warrantee 8 yrs 80k miles.
Could be a bunch of things:
-Check all grounds, search Bill Curlee's electrical sticky at the top of the page.
-Check for broken valve springs
-Check voltage for each coil pack and injector
-Check exhaust pressure at the HO2 sensors before and after the cats, before should be about 2 lbs, after should be less if you are running a stock exhaust midpipe
Please post up the What your driving, year, Z06 or not, mods etc. Also reset your DIC codes and then drive it and repost all code that come up.
I can tell you that I went down the same road and it ended up being a bad cat on the drivers side. It was covered under the original warrantee 8 yrs 80k miles.
Could be a bunch of things:
-Check all grounds, search Bill Curlee's electrical sticky at the top of the page.
-Check for broken valve springs
-Check voltage for each coil pack and injector
-Check exhaust pressure at the HO2 sensors before and after the cats, before should be about 2 lbs, after should be less if you are running a stock exhaust midpipe
Burning Brakes
Joined: Oct 2008
Posts: 898
Likes: 25
From: Dallas, TX
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Burning Brakes
Joined: Oct 2008
Posts: 898
Likes: 25
From: Dallas, TX
Unless your into modding your car, beware! Exhuast mods are just the beginning.
Burning Brakes
Joined: Oct 2008
Posts: 898
Likes: 25
From: Dallas, TX
Here is one of the posts that has the grounds shown. This is inside of the sticky, it's on the technical section at the top.
http://forums.corvetteforum.com/1572287511-post794.html
http://forums.corvetteforum.com/1572287511-post794.html
Burning Brakes
Joined: Oct 2008
Posts: 898
Likes: 25
From: Dallas, TX
I guess you could also have a broken exhaust valve spring not sure how else you might be getting the exhast smell. I ended up taking it to Chevy and asked them to check the pressure, it cost me about 100 bucks but they found the problem right away. I told them NOT to troubleshoot anything I had already checked and spoke to the tech priort o dropping the car off. He was pretty good with Vettes and worked on most that came in.
Intermediate
Joined: Jan 2010
Posts: 29
Likes: 0
From: plano tx
p300
P300 is just a random missfire code. When you replaced the coil it prob reset the comp. If you let it run a bit you will prob end up with the P305 code agian. It takes the comp a bit of time to figure the misfire out. Check the valve spring I work for a chevy dealer and Ive seen alot of these.
Burning Brakes
Joined: Oct 2008
Posts: 898
Likes: 25
From: Dallas, TX
I agree that the spring is suspect, but that's what a bunch of folks and tuner shops told me too. If the cat is plugged on one side (not uncommon for cars that have spent time in the garage and not driven until hot) the additional backpressure screws up the whole deal and the P300 sets. It is indicating multiple misfires NOT random. I watched my car misfire on the computer and it was pretty consistent on 3 or 4 cylinders. I think it was 3 on the drivers side and one sympathy misfire on the passenger.
Checking the pressure is way easier than pulling the cover.
Oh by the way, Chevy will probably tell you that they can't get a new pipe. It's $1200.00 and they don't keep many. There were only 2 in the country when mine went bad. It was a pain.
Checking the pressure is way easier than pulling the cover.
Oh by the way, Chevy will probably tell you that they can't get a new pipe. It's $1200.00 and they don't keep many. There were only 2 in the country when mine went bad. It was a pain.
Burning Brakes
Joined: Oct 2008
Posts: 898
Likes: 25
From: Dallas, TX
If you were getting a consistent P305, I wouldn't even bring up the cats, but I went on quite a goose chase to run down my problem. It started out not too bad, just the code and once it popped up the individual cylinder. Then it got worse, and started running bad. After that it all went down hill. It got to the point where I thought I would have to tow it to the dealer.
Everything in the car was perfect, except the cat. After we solved it folks came out of the woodwork telling me that it was not the first time they had seen it.
It happens when a car is only driven for short distances and the cats never get to full operating temp. The crud that the catalyst removes from the exhaust never burns off and ends up clogging the cat.
Anyway, I really hope it turns out be something simpler and cheaper than then mid-pipe. Maybe someone near you has one that you could put your hands on for cheap.
Good luck, keep us posted.
Melting Slicks
Joined: Nov 2003
Posts: 2,911
Likes: 2
From: Honolulu Hawaii
I posted up a thread on this. After searching all the chassis grounds, 02 sensors, MAF, fuel injector harness, every electrical connection, valves & springs.....it ended up being a blown header gasket. Ran OK, but not strong. Strong fuel odor from driver side, very high IAT's.
